playing online chess

Hi
can anyone help!?
While playing online chess I made my move and a couple of days later I returned to game and found that there were about three more moves which I hadnt made?
I didnt accuse my opponent of cheating as he was only responding to my supposed moves.
Consulting the moderator she says .....it is impossible,is it a browser problem ... I suggest you clear temporary internet files

Could you please tell me how to clear internet files and would anyone be able to refute the lady saying it is impossible!?
thank you
John